Optoelectronic structures having multi-level optical waveguides and methods of forming the structures

ABSTRACT

Disclosed are structures with an optical waveguide having a first segment at a first level and a second segment extending between the first level and a higher second level and further extending along the second level. Specifically, the waveguide comprises a first segment between first and second dielectric layers. The second dielectric layer has a trench, which extends through to the first dielectric layer and which has one side positioned laterally adjacent to an end of the first segment. The waveguide also comprises a second segment extending from the bottom of the trench on the side adjacent to the first segment up to and along the top surface of the second dielectric layer on the opposite side of the trench. A third dielectric layer covers the second segment in the trench and on the top surface of the second dielectric layer. Also disclosed are methods of forming such optoelectronic structures.

BACKGROUND

The structures and methods disclosed herein relate to optoelectronicsand, more particularly, to optoelectronic structures having an opticalwaveguide that provides a multi-level optical signal pathway and methodsof forming such optoelectronic structures.

More specifically, in optoelectronics and, particularly, inoptoelectronic integrated circuits, optical waveguides provide on-chipoptical signal pathways for transmitting optical signals (i.e., lightsignals) between on-chip and/or off-chip optical devices including, butnot limited to, optical fibers, optical transmitters, optical receivers,and electrical-to-optical or optical-to-electrical transducers.Generally, an optical waveguide includes a core surrounded by cladding.Both the core and the cladding comprise light-transmissive materials(e.g., light-transmissive dielectric materials); however, the corematerial(s) have a refractive index that is higher than that of thecladding material(s) so that light signals received by the opticalwaveguide are confined to and propagated along the core. Typically,optical waveguides are formed as single-level structures. That is, theyare formed with one or more linear or angled segments on a single levelof a chip (e.g., on a single horizontal plane on a chip) and, therebyonly allow communication of light signals between optical devices onthat same level. Oftentimes, however, it is necessary to communicatelight signals between optical devices at different levels (e.g., ondifferent horizontal planes on a chip), but techniques for formingmulti-level optical waveguides can be inefficient and costly. Therefore,there is a need in the art for an optoelectronic structure having amulti-level optical waveguide and an efficient and cost-effective methodof forming such an optoelectronic structure.

SUMMARY

In view of the foregoing, disclosed herein are optoelectronic structureshaving an optical waveguide comprising two discrete segments thatprovide a multi-level optical signal pathway on a chip. The opticalwaveguide can comprise a first segment at a first level and a secondsegment, which extends between the first level and a higher second leveland which further extends along the second level. Specifically, theoptical waveguide can comprise a first segment between a firstdielectric layer and a second dielectric layer. A trench can extendthrough the second dielectric layer such that it has a first sidepositioned laterally adjacent to one end of the first segment and suchthat it has a second side opposite the first side. The optical waveguidecan further comprise a second segment with a first portion and a secondportion. The first portion can be within the trench and can extend fromthe first side on the bottom adjacent to the first segment up to the topon the second side. The second portion can be continuous with the firstportion and can extend laterally onto the top surface of the seconddielectric layer. A third dielectric layer can cover the second segmentboth in the trench and on the top surface of the second dielectriclayer. Also disclosed herein are methods of forming such optoelectronicstructures.

More particularly, disclosed herein is an optoelectronic structure withan optical waveguide comprising two discrete segments (i.e., a firstsegment and a second segment) that provide a multi-level optical signalpathway on a chip.

The first segment of the optical waveguide can be on a first level and,particularly, on a first dielectric layer. A second dielectric layer canbe positioned above the first dielectric layer such that it covers thefirst segment of the optical waveguide. This second dielectric layer canhave a bottom surface immediately adjacent to the first dielectric layerand a top surface opposite the bottom surface. Additionally, this seconddielectric layer can have a trench, which extends from the top surfaceof the second dielectric layer to the bottom surface of the seconddielectric layer and which has a first side comprising a first sidewalland a second side opposite the first side and comprising a secondsidewall. The trench can specifically be positioned within the seconddielectric layer so that the first sidewall is adjacent to one end ofthe first segment. For example, the trench can be positioned such thatone end of the first segment is exposed in the lowermost portion of thefirst sidewall.

The second segment of the optical waveguide can extend from the firstlevel onto a higher second level and, particularly, onto the top surfaceof the second dielectric layer. Specifically, the second segment canhave two continuous portions (i.e., a first portion and a secondportion). The first portion can extend through the trench and,particularly, can extend from the bottom of the trench adjacent to thefirst segment on the first side up to the top surface of the seconddielectric layer on the second side (i.e., up to the top of the trenchon the second side). In one optoelectronic structure, this first portioncan line (i.e., can be positioned immediately adjacent to) a portion ofthe first dielectric layer exposed at the bottom of the trench and canalso line the second sidewall on the second side of the trench.Alternatively, the first portion can curve upward from the bottom of thetrench to the top surface of the second dielectric layer such that thedistance between the first portion and the second sidewall tapers fromthe bottom of the trench to the top surface of the second dielectriclayer. In any case, the second portion can be continuous with the firstportion and can extend onto the top surface of the second dielectriclayer (i.e., onto the second level) adjacent to the second side of thetrench and can further extend laterally away from that second side.

A third dielectric layer can be positioned on the top surface of thesecond dielectric layer, covering the second portion of the secondsegment of the optical waveguide. This third dielectric layer can alsofill the trench so as to also cover the first portion of the secondsegment of the optical waveguide.

It should be noted that to ensure proper transmission of light signalsthrough the optical waveguide, the optical waveguide and, particularly,both the first and second segments thereof will each have a higherrefractive index than the surrounding dielectric material. That is, thefirst and second segments will each have a higher refractive index thanthe first dielectric layer, the second dielectric layer and the thirddielectric layer.

Also disclosed herein are methods for forming the above-describedoptoelectronic structures with multi-level optical waveguides.

One method of forming an optoelectronic structure with a multi-leveloptical waveguide can comprise forming a first segment of an opticalwaveguide on a first dielectric layer (i.e., on a first level).Specifically, a first light-transmissive layer can be formed on thefirst dielectric layer and then etched to form a firstlight-transmissive body and, particularly, the first segment.

Then, a second dielectric layer can be formed on the first dielectriclayer so as to cover the first segment. Thus, the second dielectriclayer will have a bottom surface adjacent to the first dielectric layerand the first segment and a top surface opposite the bottom surface.

Next, a trench can be formed that extends through the second dielectriclayer from the top surface of the second dielectric layer to the bottomsurface of the second dielectric layer. Specifically, this trench can beformed so that it has a first side comprising a first sidewall and asecond side opposite the first side and comprising a second sidewall.This trench can further be formed so that the first sidewall is adjacentto one end of the first segment. For example, this trench can further beformed such that one end of the first segment is exposed at thelowermost portion of the first sidewall.

After the trench is formed, a second segment of the optical waveguidecan be formed such that it extends from the first level to a highersecond level and, particularly, onto the top surface of the seconddielectric layer. Specifically, the second segment can be formed suchthat it comprises two continuous portions (i.e., a first portion and asecond portion). The first portion can extend through the trench fromthe bottom adjacent to the first segment on the first side, along theportion of the first dielectric layer at the bottom of the trench andalong the second sidewall on the second side up to the top surface ofthe second dielectric layer. The second portion can be continuous withthe first portion and can extend onto the top surface of the seconddielectric layer (i.e., onto the second level) adjacent to the secondside of the trench and can extend laterally away from that second side.

To accomplish this, after forming the trench, a secondlight-transmissive layer can be formed so that it is on the top surfaceof the second dielectric layer and so that it also lines the bottom andsidewalls of the trench. This second light-transmissive layer can beetched so as to form a second light-transmissive body and, particularly,the second segment with the first portion and the second portion. Thatis, the second light-transmissive layer can be etched so as to definethe shape of the first portion, which extends laterally across thebottom of the trench from adjacent to the first segment at the firstsidewall to the second sidewall and which further extends along thesecond sidewall from the bottom of the trench to the top surface of thesecond dielectric layer, and so as to define the shape of the secondportion, which extends laterally from the first portion onto the topsurface of the second dielectric layer and away from the second side.

Once the second segment is formed, a third dielectric layer can beformed on the top surface of the second dielectric layer so that itcovers the second portion of the second segment of the opticalwaveguide. This third dielectric layer can also be formed so that itfills the trench, thereby covering the first portion of the secondsegment of the optical waveguide within the trench.

It should be noted that to ensure proper transmission of light signalsthrough the optical waveguide formed according to this method, theoptical waveguide and, particularly, both the first and second segmentsthereof should be formed so as to have a higher refractive index thanthe surrounding dielectric material. That is, the first and secondsegments should be formed so as to have a higher refractive index thanthe first dielectric layer, the second dielectric layer and the thirddielectric layer.

Other methods of forming optoelectronic structures with multi-leveloptical waveguides can comprise forming a first segment of an opticalwaveguide on a first dielectric layer (i.e., on a first level).Specifically, a first light-transmissive layer can be formed on thefirst dielectric layer and then etched to form a firstlight-transmissive body and, particularly, the first segment.

Then, a second dielectric layer can be formed on the first dielectriclayer so as to cover the first segment. Thus, the second dielectriclayer can have a bottom surface adjacent to the first dielectric layerand the first segment and a top surface opposite the bottom surface.

In these methods, a trench can be formed in the second dielectric layersuch that it extends from the top surface of the second dielectric layerto the bottom surface of the second dielectric layer and such that ithas a first side comprising a first sidewall and a second side oppositethe first side and comprising a second sidewall. This trench canspecifically be formed such that the first sidewall is adjacent to oneend of the first segment. For example, this trench can be formed suchthat one end of the first segment is exposed at the lowermost portion ofthe first sidewall. Additionally, a second segment of the opticalwaveguide can be formed such that it comprises two continuous portions(i.e., a first portion and a second portion). The first portion canextend through the trench from the first level to a higher second leveland, particularly, can have an end at the bottom of the trench adjacentto the first segment on the first side and can further curve upward fromthe bottom of the trench to the top surface of the second dielectriclayer such that the distance between the first portion and the secondsidewall tapers from the bottom of the trench to the top surface of thesecond dielectric layer. The second portion can be continuous with thefirst portion and can extend onto the top surface of the seconddielectric layer (i.e., onto the second level) adjacent to the secondside and can extend laterally away from that second side.

In order to form such a second segment, before the trench is formed, asecond light-transmissive layer can be formed on the second dielectriclayer and etched to form a second light-transmissive body. This secondlight-transmissive body can have an end section that partially overlaysthe end of the first segment. Then, the trench can be formed so that itis aligned below the end section of the second light-transmissive body.As result, upon formation of the trench, the end section, which isunsupported, curves downward (i.e., bends downward) into the trench,thereby forming the second segment. Alternatively, the secondlight-transmissive body can overlay the first segment and the trench canbe formed such that it is aligned below a center section of the secondlight-transmissive body. In this case, after the trench is formed, thesecond light-transmissive body is cut near the first side of the trenchsuch that the center section becomes unsupported and, as a result, thecenter section curves downward (i.e., bends) into the trench, therebyforming the second segment.

Once the second segment is formed, a third dielectric layer can beformed on the top surface of the second dielectric layer so that itcovers the second portion of the second segment of the opticalwaveguide. This third dielectric layer can also be formed so that itfills the trench, thereby covering and, specifically, surroundingexposed surfaces of the first portion of the second segment of theoptical waveguide within the trench.

It should be noted that to ensure proper transmission of light signalsthrough the optical waveguide formed according to these methods, theoptical waveguide and, particularly, both the first and second segmentsthereof should be formed so as to have a higher refractive index thanthe surrounding dielectric material. That is, the first and secondsegments should be formed so as to have a higher refractive index thanthe first dielectric layer, the second dielectric layer and the thirddielectric layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, which are notnecessarily drawn to scale and in which:

FIG. 1 is a cross-section diagram illustrating an optoelectronicstructure incorporating a multi-level optical waveguide;

FIG. 2 is a cross-section diagram illustrating another optoelectronicstructure incorporating a multi-level optical waveguide;

FIG. 3 is a flow diagram illustrating a method of forming theoptoelectronic structure of FIG. 1;

FIG. 4 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above(or of FIG. 12 below);

FIG. 5A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above(or of FIG. 12 below);

FIG. 5B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 5A;

FIG. 6A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above(or of FIG. 12 below);

FIG. 6B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 6A;

FIG. 7 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above(or of FIG. 12 below);

FIG. 8 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above;

FIG. 9 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above;

FIG. 10A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above;

FIG. 10B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 10A;

FIG. 11A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 3 above;

FIG. 11B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 11A;

FIG. 12 is a flow diagram illustrating a method of forming theoptoelectronic structure of FIG. 2;

FIG. 13 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 14A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 14B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 14A;

FIG. 15A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 15B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 15A;

FIG. 16 is a top view diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 17 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 18 is a top view diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 19 is a top view diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 20 is a top view diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 21A is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above;

FIG. 21B is a top view diagram illustrating the same partially completedoptoelectronic structure as shown in FIG. 21A;

FIG. 22 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above; and,

FIG. 23 is a cross-section diagram illustrating a partially completedoptoelectronic structure formed according to the method of FIG. 12above.

DETAILED DESCRIPTION

As mentioned above, in optoelectronics and, particularly, inoptoelectronic integrated circuits, optical waveguides provide on-chipoptical signal pathways for transmitting optical signals (i.e., lightsignals) between on-chip and/or off-chip optical devices including, butnot limited to, optical fibers, optical transmitters, optical receivers,and electrical-to-optical or optical-to-electrical transducers.Generally, an optical waveguide includes a core surrounded by cladding.Both the core and the cladding comprise light-transmissive materials(e.g., light-transmissive dielectric materials); however, the corematerial(s) have a refractive index that is higher than that of thecladding material(s) so that light signals received by the opticalwaveguide are confined to and propagated along the core. Typically,optical waveguides are formed as single-level structures. That is, theyare formed with one or more linear or angled segments on a single levelof a chip (e.g., on a single horizontal plane on a chip) and, therebyonly allow communication of light signals between optical devices onthat same level. Oftentimes, however, it is necessary to communicatelight signals between optical devices at different levels (e.g., ondifferent horizontal planes on a chip), but techniques for formingmulti-level optical waveguides can be inefficient and costly. Therefore,there is a need in the art for an optoelectronic structure having amulti-level optical waveguide and an efficient and cost-effective methodof forming such structure.

In view of the foregoing, disclosed herein are optoelectronic structureshaving an optical waveguide comprising two discrete segments thatprovide a multi-level optical signal pathway on a chip. The opticalwaveguide can comprise a first segment at a first level and a secondsegment, which extends between the first level and a higher second leveland which further extends along the second level. Specifically, theoptical waveguide can comprise a first segment between a firstdielectric layer and a second dielectric layer. A trench can extendthrough the second dielectric layer such that it has a first sidepositioned laterally adjacent to one end of the first segment and suchthat it has a second side opposite the first side. The optical waveguidecan further comprise a second segment with a first portion and a secondportion. The first portion can be within the trench and can extend fromthe first side on the bottom adjacent to the first segment up to the topon the second side. The second portion can be continuous with the firstportion and can extend laterally onto the top surface of the seconddielectric layer. A third dielectric layer can cover the second segmentboth in the trench and on the top surface of the second dielectriclayer. Also disclosed herein are methods of forming such optoelectronicstructures.

More particularly, referring to FIG. 1 and FIG. 2, disclosed herein areoptoelectronic structures 100, 200 on a substrate 101, 201 (e.g., asemiconductor substrate, such as a silicon substrate, or any othersuitable substrate). Each optoelectronic structure 100, 200 can comprisean optical waveguide 120, 220 and this optical waveguide 120, 220 cancomprise two discrete segments (i.e., a first segment 121, 221 and asecond segment 122, 222) that provide a multi-level optical signalpathway on a chip between, for example, on-chip optical devices atdifferent levels and/or between ports to off-chip optical devices atdifferent levels (not shown).

The first segment 121, 221 of the optical waveguide 120, 220 can be on afirst level and, particularly, on the top surface of a first dielectriclayer 111, 211 above the substrate 101, 201. This first dielectric layer111, 211 can be immediately adjacent to the substrate 101, 201 or,alternatively, can be separated from the substrate 101, 201 by one ormore additional layers 114 (e.g., one or more additional dielectriclayer(s)). This first segment 121, 221 can comprise, for example, afirst light-transmissive body comprising at least one light-transmissivematerial (e.g., a light-transmissive dielectric material). The firstsegment 121, 221 can have an essentially rectangular cross-sectionalshape (e.g., a square cross-sectional shape) or, alternatively, can havean essentially circular cross-sectional shape. In any case, the firstsegment 121, 221 can have a predetermined cross-sectional area. Thefirst segment 121, 221 can further have opposing ends 126-127, 226-227with one end 126, 226 being adjacent to any one of an on-chip opticaldevice on the same level or a port to an off-chip optical device (notshown). This first segment 121, 221 can be essentially linear, asillustrated. Alternatively, this first segment 121, 221 can be angled orcurved. It should be noted that any angles or curves should be wideenough to allow for light signal propagation through the first segment121, 221.

A second dielectric layer 112, 212 can be positioned above the firstdielectric layer 111, 211 such that it covers the first segment 121, 221of the optical waveguide 120, 220. This second dielectric layer 112, 212can have a bottom surface 181, 281 immediately adjacent to the firstdielectric layer 111, 211 and the first segment 121, 221 and a topsurface 182, 282 opposite the bottom surface 181, 281.

A trench 130, 230 can extend through the second dielectric layer 112,212 from the top surface 182, 282 to the bottom surface 181, 281. Thistrench 130, 230 can have a first side 131, 231 comprising a firstsidewall 133, 233 and a second side 132, 232 opposite the first side131, 231 and comprising a second sidewall 134, 234. The trench 130, 230can specifically be positioned within the second dielectric layer 112,212 so that the first side 131, 231 and, particularly, the firstsidewall 133, 233 is adjacent to the end 127, 227 of the first segment121, 221. For example, the trench 130, 230 can be positioned such thatthe end 127, 227 of the first segment 121, 221 is exposed in thelowermost portion of the first sidewall 133, 233 at the bottom 135, 235of the trench 130, 230.

The second segment 122, 222 of the optical waveguide 120, 220 can extendfrom the first level up to and onto a higher second level. Specifically,the second segment 122, 222 of the optical waveguide 120, 220 can haveopposing ends 128-129, 228-229 and two continuous portions (i.e., afirst portion 123, 223 and a second portion 124, 224) that extendbetween the two opposing ends 128-129. The second segment 122, 222 cancomprise a second light-transmissive body comprising at least onelight-transmissive material. For example, the second segment 122, 222can comprise the same light-transmissive material(s) as the firstsegment 121, 221. The second segment 122, 222 can have an essentiallythe same cross-sectional shape (e.g., an essentially rectangularcross-sectional shape, such as a square cross-sectional shape, or,alternatively, an essentially circular cross-sectional shape) andcross-sectional area as the first segment 121, 221.

The first portion 123, 223 of the second segment 122, 222 can be withinthe trench 130, 230 with an end 128, 228 at the bottom 135, 235 on thefirst side 131, 231 such that it is adjacent to the first sidewall 133,233 and, particularly, such that it is adjacent to the end 127, 227 ofthe first segment 121, 221. That is, the first portion 123, 223 of thesecond segment 122, 222 can be in end-to-end alignment with the firstsegment 121, 221. The first portion 123, 223 can further be positionedimmediately adjacent to (i.e., in contact with) the first segment 121,221 (i.e., the adjacent ends 127, 227 and 128, 228 of the first segment121, 221 and of the first portion 123, 223 of the second segment 122,222, respectively, can meet). Alternatively, the first portion 123, 223can be separated from, but less than a predetermined distance 195, 295from, the first segment 121, 222 (i.e., the adjacent ends 127, 227 and128, 228 of the first segment 121, 221 and of the first portion 123, 223of the second segment 122, 222, respectively, can be spaced no more thana predetermined distance 195, 295 apart). This predetermined distance195, 295 can be the maximum separation distance allowable for light topropagate between the first segment 121, 221 and the second segment 122,222. Those skilled in the art will recognize that this maximumseparation distance will vary depending upon a variety of factorsincluding, but not limited to, the materials used, the cross-sectionalarea of the segments, the frequency of the light signals, etc. The firstportion 123, 223 of the second segment 122, 222 can further extend fromthe bottom 135, 235 of the trench 130, 230 on the first side 131, 231across the trench 130, 230 to the second side 132, 232 and,particularly, up to the top surface 182, 282 of the second dielectriclayer 112, 212 on the second side 132, 232 of the trench 130, 230 (i.e.,up to the top of the trench 130, 230 on the second side 132, 232).

Specifically, as shown in the optoelectronic structure 100 of FIG. 1,this first portion 123 of the second segment 122 can line (i.e., can bepositioned immediately adjacent to) a portion of the first dielectriclayer 111 exposed at the bottom 135 of the trench 130 and can extendlaterally from adjacent to the first sidewall 133 to the second sidewall134. This first portion 123 can further line (i.e., can be positionedimmediately adjacent to) the second sidewall 134 on the second side 132of the trench 130 and can extend along the second sidewall 134 from thebottom 135 of the trench 130 to the top surface 182 of the seconddielectric layer 112 (i.e., to the top of the trench 130 on the secondside 132). Alternatively, as shown in the optoelectronic structure 200of FIG. 2, the first portion 223 of the second segment 222 can extendlaterally from the bottom 235 of the trench 230 adjacent to the firstsidewall 233 toward the second sidewall 234 and can curve upward fromthe bottom 235 of the trench 230 toward the top surface 282 of thesecond dielectric layer 212. This upward curve can begin some distanceaway from the second sidewall 234 (e.g., at some point near the centerof the trench 230) such that the distance between the first portion 223and the second sidewall 234 tapers from the bottom 235 of the trench 230to the top surface 282 of the second dielectric layer 212.

In any case, the second portion 124, 224 of the second segment 122, 222of the optical waveguide 120, 220 can be continuous with the firstportion 123, 223 and can extend over the edge of the trench 130, 230 onthe second side 132, 232 onto the top surface 182, 282 of the seconddielectric layer 112, 212 (i.e., onto the higher second level). Thissecond portion 124, 224 can further extend laterally away from thatsecond side 132, 232 of the trench 130, 230. The second portion 124, 224can further have an end 129, 229 positioned adjacent to any one of anon-chip optical device at the same level or a port to an off-chipoptical device (not shown). This second portion 124, 224 of the secondsegment 122, 222 can be essentially linear, as illustrated.Alternatively, this second portion 124, 224 of the second segment 122,222 can be angled or curved. It should be noted that any angles orcurves should be wide enough to allow for light signal propagationthrough the second segment 122, 222.

It should be noted that in the optoelectronic structures 100 and 200 ofFIGS. 1 and 2, respectively, the first sidewall 133, 233 and the secondsidewall 134, 234 could be angled (i.e., sloped) relative to the bottomsurface 181, 281 and top surface 182, 282 of the second dielectric layer112, 212. Specifically, in the case of the optoelectronic structure 100of FIG. 1, wherein the first portion 123 of the second segment 122 linesthe bottom 135 and the second sidewall 134 of the trench 130 (i.e.,wherein the shape of the first portion 123 is defined by the profile ofthe trench 130), the sidewalls should be angled (as opposed to beingnormal (i.e., perpendicular)) relative to the bottom surface 181 and thetop surface 182 of the second dielectric layer 112. Furthermore, theangle of the second sidewall 134 of the trench 130 relative to thebottom and top surfaces 181-182 of the second dielectric layer 112should be wide enough (e.g., greater than 90°, between 120° and 170°,etc.) to allow for continued propagation of light signals through thecurves in the first portion 123 both in the bottom 135 of the trench 130and around the edge of the trench 130 at the top surface 182 of thesecond dielectric layer 112. In the case of the optoelectronic structure200 of FIG. 2, the first and second sidewalls 233-234 can be angled(i.e., sloped) relative to bottom and top surfaces 281-282; however,since the first portion 223 of the second segment 222 is notself-aligned with the second sidewall 234 (i.e., since the shape of thefirst portion 223 is not defined by the profile of the trench 230), thefirst and second sidewalls 233-234 can, alternatively, be perpendicularto the bottom and top surfaces 281-282 of the second dielectric layer212, curved, etc.

The optoelectronic structure 100, 200 can further comprise a thirddielectric layer 113, 213 positioned on the top surface 182, 282 of thesecond dielectric layer 112, 212, covering the second portion 124, 224of the second segment 122, 222 of the optical waveguide 120, 220. Thisthird dielectric layer 113, 213 can also fill the trench 130, 230 so asto also cover (and surround, if applicable, as illustrated in FIG. 2)the first portion 123, 223 of the second segment 122, 222 of the opticalwaveguide 120, 220 contained within the trench 130, 230.

As mentioned above, the first segment 121, 221 and the second segment122, 222 of the optical waveguide 120, 220 can have specific refractiveindices and, if the light-transmissive material(s) used are the same,the refractive indices will be the same. Furthermore, to ensure propertransmission of light signals through the optical waveguide 120, 220,the refractive indices of the first segment 121, 221 and the secondsegment 122, 222, which function as the core, must be higher than therefractive indices of surrounding dielectric material (i.e., whichfunctions as the cladding). That is, the first segment 121, 221 andsecond segment 122, 222 can each comprise light-transmissive material(s)(e.g., light-transmissive dielectric materials) with a higher refractiveindex than the first dielectric layer 111, 211, the second dielectriclayer 112, 212 and the third dielectric layer 113, 213.

Optionally, the first dielectric layer 111, 211, the second dielectriclayer 112, 212, the third dielectric layer 113, 213 and/or anyadditional dielectric layers 114, 214 can comprise different dielectricmaterials. For example, the first dielectric layer 111, 211 can comprisea first dielectric material and the second dielectric layer 112, 212 cancomprise a second dielectric material, which is different from the firstdielectric material and which, during processing and, particularlyduring trench formation, can be selectively etched over the firstdielectric material (see the more detailed discussion below with regardto the methods). Furthermore, the second dielectric layer 112, 212, thethird dielectric layer 113, 213 and the additional dielectric layer(s)114, 214 can comprise the same dielectric material or differentdielectric materials.

Therefore, in one exemplary optoelectronic structure 100, 200, the firstdielectric layer 111, 211 can comprise silicon nitride, having arefractive index of approximately 2; the second dielectric layer 112,212, third dielectric layer 113, 213 and an additional dielectric layer114, 214 between the substrate 101, 201 and the first dielectric layer111, 211 can comprise silicon dioxide, having a refractive index ofapproximately 1.5; and, the first segment 121, 221 and second segment122, 222 of the optical waveguide 120, 220 can comprise silicon (Si)having a refractive index of approximately 3.5 or any of the followingmaterials having appropriate refractive indices for the opticalwaveguide structures: phosphorous-doped and/or boron-doped siliconoxide, germanium-doped silicon oxide, silicon oxynitride (SiON), silicongermanium (SiGe), or any of various different light-transmissivepolymers. It should be understood that the list of exemplary materialsmentioned above is not intended to be limiting. Those skilled in the artwill recognize that, alternatively, other material combinations suitablefor use in optoelectronic structures and, particularly, suitable for useas core and cladding materials in optical waveguides could be used.

Also disclosed herein are methods for forming the above-describedoptoelectronic structures 100, 200 with multi-level optical waveguides120, 220, as shown in FIGS. 1 and 2.

Referring to the flow diagram of FIG. 3, one method of forming anoptoelectronic structure 100 with a multi-level optical waveguide 120,as shown in FIG. 1, can comprise providing a substrate 101 (e.g., asemiconductor substrate, such as a silicon substrate, or any othersuitable substrate) (302, see also FIG. 4).

A first dielectric layer 111 can be formed (e.g., deposited) above thesubstrate 101 and, optionally, this first dielectric layer 111 can beformed above one or more additional layers (e.g., additional dielectriclayers 114) on the substrate 101 (304, see also FIG. 4). After the firstdielectric layer 111 is deposited, an optional chemical-mechanicalpolishing (CMP) process may be performed in order to ensure that the topsurface of the first dielectric layer 111 is essentially planar.

A first segment 121 of an optical waveguide 120 can be formed on the topsurface of the first dielectric layer 111 (i.e., on a first level)(306-308, see also FIG. 4, FIGS. 5A-5B and FIGS. 6A-6B). Specifically, afirst light-transmissive layer 140 can be formed (e.g., deposited) onthe first dielectric layer 111 (306, see also FIG. 4). This firstlight-transmissive layer 140 can comprise at least one transmissivematerial (e.g., a light-transmissive dielectric material) having aspecific refractive index. After the first light-transmissive layer 140is deposited, an optional chemical-mechanical polishing (CMP) processmay be performed in order to ensure that the top surface of the firstlight-transmissive layer 140 is essentially planar and to further ensurethat the first light-transmissive layer 140 and, thereby the firstsegment of the optical waveguide 120 will have a desired thickness (seedetailed discussion below regarding the dimensions of the opticalwaveguide). A mask 171 can then be formed on the firstlight-transmissive layer 140 (e.g., using conventional photolithographicpatterning techniques) (see FIGS. 5A-5B) and exposed portions of thefirst light-transmissive layer 140 can be etched away to form a firstlight-transmissive body and, particularly, the first segment 121 of theoptical waveguide 120 (308, see also FIGS. 6A-6B).

It should be noted that these process 306-308 should be performed suchthat the first segment 121 has an essentially rectangularcross-sectional shape (e.g., a square cross-sectional shape) with apredetermined cross-sectional area. These processes 306-308 can furtherbe performed such that the first segment 121 has opposing ends 126-127,wherein one end 126 of the first segment 121 is, for example, adjacentto any one of an on-chip optical device on the same level or a port toan off-chip optical device (not shown). Additionally, these processes306-308 can be performed such that the first segment 121 is essentiallylinear, as illustrated, or, alternatively, such that the first segment121 is angled or curved. It should be noted that any angles or curvesshould be wide enough to allow for light signal propagation through thefirst segment 121.

After the first segment 121 of the optical waveguide 120 is formed onthe first dielectric layer 111, the mask 171 can be selectively removedand a second dielectric layer 112 can be formed (e.g., deposited) on thefirst dielectric layer 111 so as to cover the first segment 121 (310,see also FIG. 7). Thus, the second dielectric layer 112 will have abottom surface 181 adjacent to the first dielectric layer 111 and thefirst segment 121. This second dielectric layer 112 will further have atop surface 182 opposite the bottom surface 181. This second dielectriclayer 112 can be preselected so that it comprises a different dielectricmaterial than the first dielectric layer 111 and, particularly, so thatit can be etched selectively over the first dielectric layer at process312, discussed below. After the second dielectric layer 112 isdeposited, an optional chemical-mechanical polishing (CMP) process maybe performed in order to ensure that the top surface 182 of the seconddielectric layer 112 is substantially planar and to further ensure thatthe second dielectric layer 112 has a desired thickness (see detaileddiscussion below regarding the dimensions of the optical waveguide).

A trench 130 can subsequently be formed in the second dielectric layer112 such that it extends through the second dielectric layer 112 fromthe top surface 182 to the bottom surface 181 (312, see also FIG. 8).Specifically, a mask can be formed on the second dielectric layer 112(e.g., using conventional lithographic patterning techniques) and anexposed portion of the second dielectric layer 112 can be etched. Themask patterning and etch processes can be performed such that the trench130 extends to the first dielectric layer 111 (i.e., the firstdielectric layer 111 functions as an etch stop layer) and such that thetrench 130 has a first side 131 comprising a first sidewall 133 and asecond side 132 opposite the first side 131 and comprising a secondsidewall 134. The mask patterning and etch processes can further beperformed such that the first side 131 of the trench 130 and,particularly, the first sidewall 133 is adjacent to one end 127 of thefirst segment 121. For example, the mask patterning and etch processescan be performed so that one end 127 of the first segment 121 is exposedat the lowermost portion of the first sidewall 133 at the bottom 135 ofthe trench 130. Additionally, the mask patterning and etch processes canbe performed such that the first and second sidewalls 133-134 are angled(i.e., sloped) relative to the bottom and top surfaces 181-182 of thesecond dielectric layer 112, as opposed to being normal (i.e.,perpendicular) relative thereto (see more detailed discussion below).

After the trench 130 is formed, a second segment 122 of the opticalwaveguide 120 can be formed such that it extends from the first level onthe first dielectric layer 111 adjacent to the first segment 121 upthrough the trench 130 and onto a higher second level and, particularly,onto the top surface 182 of the second dielectric layer 112 (314-316,see also FIG. 9, FIGS. 10A-10B and FIGS. 11A-11B). Specifically, afterforming the trench 130, a second light-transmissive layer 150 can beformed (e.g., conformally deposited) on the top surface 182 of thesecond dielectric layer 112 and lining the bottom 135 and sidewalls133-134 of the trench 130 (314 also FIG. 9). The secondlight-transmissive layer 150 can comprise at least onelight-transmissive material having a specific refractive index. Forexample, the second light-transmissive layer 150 can comprise the samelight-transmissive material(s) as used in forming the first segment 121.A mask 172 can then be formed on the second light-transmissive layer 150(e.g., using conventional lithographic patterning techniques) (see FIGS.10A-10B) and an exposed portion of the second light-transmissive layer150 can be etched to form a second light-transmissive body and,particularly, the second segment 122 of the optical waveguide 120,wherein the second segment 122 can have essentially the samecross-sectional shape and size (i.e., the same cross-sectional area) asthe first segment 121 (316, see also FIGS. 11A-11B). The processes314-316 can be performed such that the second segment 122 comprisesopposing ends 128-129 with one end 128 being adjacent to the end 127 ofthe first segment 121 on the first level and another end 129 on thesecond level and such that the second segment 122 comprises twocontinuous portions (i.e., a first portion 123 and a second portion 124)between the opposing ends 128-129.

Specifically, with regard to the first portion 123 of the second segment122 of the optical waveguide 120, the processes 314-316 can further beperformed such that the first portion 123 has an end 128, which is inthe trench 130 at the bottom 135 on the first side 131 adjacent to theend 127 of the first segment 121 (i.e., such that it is in end-to-endalignment with the first segment 121). These processes 314-316 can alsobe performed such that the first portion 123 is positioned immediatelyadjacent to (i.e., in contact with) the first segment 121 (i.e., suchthat adjacent ends 127 and 128 of the first segment 121 and of the firstportion 123 of the second segment 122, respectively, meet).Alternatively, these processes 314-316 can be performed such that thefirst portion 123 is separated from, but less than a predetermineddistance 195 from, the first segment 121 (i.e., such that adjacent ends127 and 128 of the first segment 121 and of the first portion 123 of thesecond segment 122, respectively, are spaced no more than apredetermined distance 195 apart). This predetermined distance 195 canbe the maximum separation distance allowable for light to propagatebetween the segments. Those skilled in the art will recognize that thismaximum separation distance will vary depending upon a variety offactors including, but not limited to, the materials used, thecross-sectional area of the segments, the frequency of the lightsignals, etc. The processes 314-316 can further be performed such thatthe first portion 123 lines (i.e., is positioned immediately adjacentto) the bottom 135 of the trench 130, extending laterally from adjacentto the first sidewall 133 to the second sidewall 134, and further lines(i.e., is positioned immediately adjacent to) the second sidewall 134 onthe second side 132 of the trench 130, extending upward along the secondsidewall 134 from the bottom 135 of the trench 130 to the top surface182 of the second dielectric layer 112.

With regard to the second portion 124 of the second segment 122 of theoptical waveguide 120, the processes 314-316 can be performed such thatthe second portion 124 is continuous with the first portion 123, extendsover the edge on the second side 132 of the trench 130 onto the topsurface 182 of the second dielectric layer 112 (i.e., onto the secondlevel), and further extends laterally away from the trench 130 to, forexample, an on-chip optical device on the same level or a port to anoff-chip optical device (not shown) adjacent to the end 129 of thesecond segment 122. Furthermore, these processes 314-316 can beperformed so that the second portion 124 is essentially linear, asillustrated, or, alternatively, so that the second portion 124, isangled or curved. It should be noted that any angles or curves should bewide enough to allow for light signal propagation through the secondsegment 122.

In any case, the processes 314-316 can be performed such that the secondsegment 122 has essentially the same cross-sectional shape (e.g., anessentially rectangular cross-sectional shape, such as a squarecross-sectional shape) with the same predetermined cross-sectional areaas the first segment 121.

It should be noted that in this method, since the first portion 123 ofthe second segment 122 lines the bottom 135 and the second sidewall 134of the trench 130 (i.e., since the shape of the first portion 123 isdefined by the profile of the trench 130), the trench 130 should beformed at process 312 such that the sidewalls 133-134 are angled, asopposed to being normal (i.e., perpendicular), relative to the bottomsurface 181 and the top surface 182 of the second dielectric layer 112.Furthermore, the angle of the second sidewall 134 relative to the bottomand top surfaces 181-182 of the second dielectric layer 112 should bewide enough (e.g., greater than 90°, between 120° and 170°, etc.) toallow for continued propagation of light signals in the resultingoptical waveguide 120 through the curves in the first portion 123 bothin the bottom 135 of the trench 130 and around the edge of the trench130 at the top surface 182 of the second dielectric layer 112. Oneexemplary technique for etching a trench with angled sidewalls in adielectric layer, such as silicon dioxide, comprises a combination ofshort oxygen (O₂) ash steps and oxide etch steps. The oxygen (O₂) ashand oxide etch steps can be alternated in order to meet a desired angleof slope. It should be understood that this exemplary technique isprovided for illustration purposes and is not intended to be limiting.Any other suitable technique for forming a trench with angled sidewallsin a dielectric layer could be used and the techniques may varydepending upon the dielectric material used.

After the second segment 122 is formed, the mask 172 can be selectivelyremoved and a third dielectric layer 113 can formed (e.g., deposited)over the top surface 182 of the second dielectric layer 112 (318, seealso FIG. 1). Specifically, the third dielectric layer 113 can be formedso that it covers the second portion 124 of the second segment 122 ofthe optical waveguide 120 on the top surface 182 of the seconddielectric layer 112 and also so that it fills the trench 130, therebycovering the first portion 123 of the second segment 122 of the opticalwaveguide 120 contained within the trench 130. After the thirddielectric layer 113 is deposited an optional chemical-mechanicalpolishing (CMP) step may be performed in order to ensure that the topsurface of the third dielectric layer 113 is essentially planar.

As mentioned above, the first and second segments 121-122 of the opticalwaveguide 120 can have specific refractive indices and, if thelight-transmissive material(s) used to form the two discrete segments atprocesses 306-316 are the same, the refractive indices will be the same.Furthermore, to ensure proper transmission of light signals through theresulting optical waveguide 120, the refractive indices of the first andsecond segments 121-122, which function as the core of the opticalwaveguide 120, must be higher than the refractive indices of thesurrounding dielectric material (i.e., which function as the cladding ofthe optical waveguide 120). That is, the first and second segments121-122 should be formed so that they comprise light-transmissivematerial(s) (e.g., light-transmissive dielectric materials) with ahigher refractive index than the first dielectric layer 111, the seconddielectric layer 112 and the third dielectric layer 113.

Optionally, the first dielectric layer 111 formed at process 304, thesecond dielectric layer 112 formed at process 310, the third dielectriclayer formed at process 318 and/or any additional dielectric layers(e.g., formed on the substrate 101 before formation of the firstdielectric layer 111 or formed above the third dielectric layer 113) cancomprise different dielectric materials. For example, the firstdielectric layer 111 formed at process 304 can comprise a firstdielectric material and the second dielectric layer 112 formed atprocess 310 can comprise a second dielectric material, which isdifferent from the first dielectric material and which, duringprocessing and, particularly during trench formation at process 312, canbe selectively etched over the first dielectric material. Furthermore,the second dielectric layer 112 formed at process 310, the thirddielectric layer 113 formed at process 318 and any additional dielectriclayer(s) 114 can comprise the same dielectric material or differentdielectric materials.

Therefore, in one exemplary method of forming the optoelectronicstructure 100, the first dielectric layer 111 can comprise siliconnitride, having a refractive index of approximately 2; the seconddielectric layer 112, third dielectric layer 113 and an additionaldielectric layer 114 between the substrate 101 and the first dielectriclayer 111 can comprise silicon dioxide, having a refractive index ofapproximately 1.5; and, the light-transmissive layers used to form thefirst segment 121 and second segment 122 can comprise silicon (Si)having a refractive index of approximately 3.5 or any of the followingmaterials having appropriate refractive indices for the opticalwaveguides structures: phosphorous-doped and/or boron-doped siliconoxide, germanium-doped silicon oxide, silicon oxynitride (SiON), silicongermanium (SiGe), or any of various different light-transmissivepolymers. It should be understood that the list of exemplary materialsmentioned above is not intended to be limiting. Those skilled in the artwill recognize that, alternatively, other material combinations suitablefor use in optoelectronic structures and, particularly, suitable for useas core and cladding materials in optical waveguides could be used.

Referring to the flow diagram of FIG. 12, methods of forming anoptoelectronic structure 200 with a multi-level optical waveguide 220,as shown in FIG. 2, can comprise providing a substrate 201 (e.g., asemiconductor substrate, such as a silicon substrate, or any othersuitable substrate) (1202, see also FIG. 4).

A first dielectric layer 211 can be formed (e.g., deposited) above thesubstrate 201 and, optionally, this first dielectric layer 211 can beformed above one or more additional layers (e.g., additional dielectriclayers 214) on the substrate 201 (1204, see also FIG. 4). After thefirst dielectric layer 211 is deposited, an optional chemical-mechanicalpolishing (CMP) process may be performed in order to make the topsurface of the first dielectric layer 211 essentially planar.

A first segment 221 of an optical waveguide 220 can be formed on the topsurface of the first dielectric layer 211 (i.e., on a first level)(1206-1208, see also FIG. 4, FIGS. 5A-5B and FIGS. 6A-6B). Specifically,a first light-transmissive layer 240 can be formed (e.g., deposited) onthe first dielectric layer 211 (1206, see also FIG. 4). This firstlight-transmissive layer 240 can comprise at least one transmissivematerial (e.g., a light-transmissive dielectric material) having aspecific refractive index. After the first light-transmissive layer 240is deposited, an optional chemical-mechanical polishing (CMP) processmay be performed in order to ensure that the top surface of the firstlight-transmissive layer 240 is essentially planar and to further ensurethat the first light-transmissive layer 240 and, thereby the firstsegment of the optical waveguide 220 has a desired thickness (seedetailed discussion below regarding the dimensions of the opticalwaveguide). A mask 271 can then be formed on the firstlight-transmissive layer 240 (e.g., using conventional photolithographicpatterning techniques) (see FIGS. 5A-5B) and exposed portions of thefirst light-transmissive layer 240 can be etched away to form a firstlight-transmissive body and, particularly, the first segment 221 of theoptical waveguide 220 (1208, see also FIGS. 6A-6B).

It should be noted that these process 1206-1208 should be performed suchthat the first segment 221 has an essentially rectangularcross-sectional shape (e.g., a square cross-sectional shape) with apredetermined cross-sectional area. These processes 1206-1208 canfurther be performed such that the first segment 221 has opposing ends226-227, wherein one end 226 of the first segment 221 is, for example,adjacent to any one of an on-chip optical device on the same level or aport to an off-chip optical device (not shown). Additionally, theseprocesses 1206-1208 can be performed such that the first segment 221 isessentially linear, as illustrated, or, alternatively, such that thefirst segment 221 is angled or curved. It should be noted that anyangles or curves should be wide enough to allow for light signalpropagation through the first segment 221.

After the first segment 221 of the optical waveguide 220 is formed onthe first dielectric layer 211, the mask 271 can be selectively removedand a second dielectric layer 212 can be formed (e.g., deposited) on thefirst dielectric layer 211 so as to cover the first segment 221 (1210,see also FIG. 7). Thus, the second dielectric layer 212 will have abottom surface 281 adjacent to the first dielectric layer 211 and thefirst segment 221. This second dielectric layer 212 will further have atop surface 282 opposite the bottom surface 281. This second dielectriclayer 212 can be preselected so that it comprises a different dielectricmaterial than the first dielectric layer 211 and, particularly, so thatit can be etched selectively over the first dielectric layer at process1212, discussed below. After the second dielectric layer 212 isdeposited, an optional chemical-mechanical polishing (CMP) process maybe performed in order to ensure that the top surface 282 of the seconddielectric layer 212 is essentially planar and to further ensure thatthe second dielectric layer 212 has a desired thickness (see detaileddiscussion below regarding the dimensions of the optical waveguide).

In these methods, a trench 230, as illustrated in FIG. 2, can be formedin the second dielectric layer 212 such that it extends from the topsurface 282 to the bottom surface 281 of the second dielectric layer 212and such that it has a first side 231 comprising a first sidewall 233and a second side 232 opposite the first side 231 and comprising asecond sidewall 234. This trench 230 can specifically be formed suchthat the first sidewall 233 is adjacent to one end 227 of the firstsegment 221. For example, this trench 230 can be formed such that oneend 227 of the first segment 221 is exposed at the lowermost portion ofthe first sidewall 233 at the bottom 235 of the trench 230.Additionally, a second segment 222 of the optical waveguide can beformed such that it comprises opposing ends 228-229 and two continuousportions (i.e., a first portion 223 and a second portion 224) betweenthe opposing ends 228-229. Specifically, the second segment 222 can beformed such that the first portion 223 extends through the trench 230from the first level to a higher second level and, particularly, suchthat the first portion 223 has the end 228 at the bottom 235 of thetrench 230 adjacent to the first segment 221 on the first side 231 andfurther curves upward from the bottom 235 of the trench 230 to the topsurface 282 of the second dielectric layer 212 such that the distancebetween the first portion 223 and the second sidewall 234 tapers fromthe bottom 235 of the trench 230 to the top surface 282 of the seconddielectric layer 212. The second segment 222 can further be formed suchthat the second portion 224 is continuous with the first portion 223,extends over the edge on the second side 232 of the trench 230 onto thetop surface 282 of the second dielectric layer 212 (i.e., onto thesecond level), and further extends laterally away from the trench 230to, for example, an on-chip optical device on the same level or a portto an off-chip optical device (not shown) adjacent to the end 229 of thesecond segment 222.

More specifically, in order to form such a second segment 222, beforethe trench is formed, a second light-transmissive layer 250 can beformed (e.g., deposited) on the second dielectric layer 212 (1212, seealso FIG. 13). The second light-transmissive layer 250 can comprise atleast one light-transmissive material having a specific refractiveindex. For example, the second light-transmissive layer 250 can comprisethe same light-transmissive material(s) as used in forming the firstsegment 221. After the second light-transmissive layer 250 is deposited,an optional chemical-mechanical polishing (CMP) process may be performedin order to ensure that the top surface of the second light-transmissivelayer 250 is essentially planar and to further ensure that the secondlight-transmissive layer 250 and, thereby the second segment of theoptical waveguide 220 will have a desired thickness (see detaileddiscussion below regarding the dimensions of the optical waveguide). Thesecond light-transmissive layer 250 can subsequently be etched to form asecond light-transmissive body 251, which has essentially the samecross-sectional shape (e.g., an essentially rectangular cross-sectionalshape, such as a square cross-sectional shape) with the samepredetermined cross-sectional area as the first segment 221. Thedifferent methods for forming the optoelectronic structure 200 of FIG. 2disclosed herein vary with regard to the length of this secondlight-transmissive body.

For example, in one method, a mask 272 can then be formed on the secondlight-transmissive layer 250 (e.g., using conventional lithographicpatterning techniques) (see FIGS. 14A-14B) and an exposed portion of thesecond light-transmissive layer 250 can be etched to the top surface 282of the second dielectric layer 212 to form a second light-transmissivebody 251, having essentially the same cross-sectional shape and the samecross-sectional area as the first segment 221 (1214, see also FIGS.15A-15B). The mask patterning and etch processes can be performed suchthat the second light-transmissive body 251 has an end section 252 thatpartially overlays the end 227 of the first segment 221 by a specificdistance 290. After the second light-transmissive body 251 is formed,the mask 272 can be selectively removed.

In this method, a trench 230 can then be formed in the second dielectriclayer 212 so that it is aligned below the end section 252 of the secondlight-transmissive body 251 and adjacent to the end 227 of the firstsegment 221 (1216, see also FIG. 16 and FIG. 17). Specifically, a mask273 can be formed (e.g., using conventional lithographic patterningtechniques) on the second dielectric layer 212 and on the secondlight-transmissive body 251 with an opening 274 that exposes the endsection 252 of the second light-transmissive body 251 as well asdielectric material 275 immediately adjacent to that end section 252(see FIG. 16). Then, an etch process can be performed in order to removedielectric material from below the end section 252 and to, thereby forma trench 230, which extends to the first dielectric layer 211 (i.e., thefirst dielectric layer 211 functions as an etch stop layer) and whichhas a first side 231 comprising a first sidewall 233 adjacent to the end227 of the first segment 221 and a second side 232 opposite the firstside 131 and comprising a second sidewall 234 (see FIG. 17). Forexample, the mask patterning and etch processes can be performed so thatthe end 227 of the first segment 221 is exposed at the lowermost portionof the first sidewall 233 at the bottom 235 of the trench 230.Additionally, the mask patterning and etch processes can be performed sothat the first and second sidewalls 233-234 are angled (i.e., sloped) orcurved relative to the bottom and top surfaces 281-282 of the seconddielectric layer 212, as opposed to being normal (i.e., perpendicular)relative thereto. Exemplary etch processes that can be used can include,for example, a wet chemical hydrofluoric acid (HF)-based etch process ora dry reactive-ion etch (RIE) process. As a result, upon formation ofthe trench 230, the end section 252, which becomes unsupported, curvesdownward (i.e., bends downward) into the trench 230, thereby forming thesecond segment 222 of the optical waveguide 220, wherein the firstportion 223 of the second segment 222 corresponds to the end section 252of the second light-transmissive body 251, which is unsupported andwhich bends into the trench 230, and the second portion 224 of thesecond segment 222 corresponds to the supported section of the secondlight-transmissive body 251, which remains on the top surface 282 of thesecond dielectric layer 212 adjacent to the second side 232 of thetrench 230.

It should be noted that, before the second light-transmissive body 251is formed, specific dimensions of the second light-transmissive body 251and the trench 230 should be determined to ensure that, when the trench230 is formed and the unsupported end section 252 bends downward, theunsupported end section 252 lands on the bottom 235 of the trench 230 inend-to-end alignment with the first segment 221 either immediatelyadjacent to or at least less than a predetermined distance 295 from theend 227 of the first segment 221. The predetermined distance 295 can bethe maximum separation distance allowable for light to propagate betweenthe segments. Those skilled in the art will recognize that this maximumseparation distance will vary depending upon a variety of factorsincluding, but not limited to, the materials used, the cross-sectionalarea of the segments, the frequency of the light signals, etc. Thedimensions can include, but are not limited to, the cross-sectional areaof the second light-transmissive body 251, the width and height of thesecond light-transmissive body 251, the specific length of the endsection 252 of the second light-transmissive body 251 that will beunsupported over the trench 230, the specific distance 290 by which theend section 252 will partially overlay the first segment 221, the lengthof the trench 230 and the depth of the trench 230 (i.e., the thicknessof the second dielectric layer 212).

The following expressions can be used to estimate the deflection of theunsupported end section (i.e., the amount that the end section will bendonce it becomes unsupported):

$\begin{matrix}{{{\Delta\; Z} = \frac{{Wl}^{3}}{8\;{EI}}},} & (1) \\{{I = {{wd}^{3}\text{/}12}},{and}} & (2) \\{{W = {\rho\;{wdlg}}},} & (3)\end{matrix}$where αZ is the deflection of the unsupported section (i.e., the amountof bend in the unsupported section), I is the second moment of inertiaof the unsupported section, W is load on the unsupported section, E isYoung's modulus, w is width of the unsupported section, d is thicknessof the unsupported section, l is the length of the unsupported section,and g is standard gravity.

Alternatively, in another method, a mask 276 can be formed on the secondlight-transmissive layer 250 (e.g., using conventional lithographicpatterning techniques) (see FIG. 18) and an exposed portion of thesecond light-transmissive layer 250 can be etched to the top surface 282of the second dielectric layer 212 to form a second light-transmissivebody 255, having essentially the same cross-sectional shape andcross-sectional area as the first segment 221 (1220, see also FIG. 19).The mask patterning and etch processes can be performed such that thesecond light-transmissive body 255 overlays the first segment 221. Afterthe second light-transmissive body 255 is formed, the mask 276 can beselectively removed.

In this method, a trench 230 can then be formed in the second dielectriclayer 212 so that it is aligned below a center section 256 of the secondlight-transmissive body 255, which is offset from but adjacent to theend 227 of the first segment 221 (1222, see also FIG. 20 and FIGS.21A-21B). Specifically, a mask 277 can be formed (e.g., usingconventional lithographic patterning techniques) on the seconddielectric layer 212 and on the second light-transmissive body 255 withan opening 278 that exposes the center section 256 of the secondlight-transmissive body 255 as well as dielectric material 279immediately adjacent to that center section 256 (see FIG. 20). Then, anetch process can be performed in order to remove dielectric materialfrom below the center section 256, thereby forming a trench 230, whichextends to the first dielectric layer 211 (i.e., the first dielectriclayer 211 functions as an etch stop layer) and which has a first side231 comprising a first sidewall 233 adjacent to the end 227 of the firstsegment 221 and a second side 232 opposite the first side 231 andcomprising a second sidewall 234 (see FIGS. 21A-21B). For example, themask patterning and etch processes can be performed so that the end 227of the first segment 221 is exposed at the lowermost portion of thefirst sidewall 233 at the bottom 235 of the trench 230. Additionally,the mask patterning and etch processes can be performed such that thefirst and second sidewalls 233-234 are angled (i.e., sloped) or curvedrelative to the bottom and top surfaces 281-282 of the second dielectriclayer 212, as opposed to being normal (i.e., perpendicular) relativethereto. Exemplary etch processes that can be used can include, forexample, a wet chemical hydrofluoric acid (HF)-based etch process or adry reactive-ion etch (RIE) process. After the trench 230 is formed, themask 277 can be selectively removed.

In this case, after the trench 230 is formed, the center section 256 ofthe second light-transmissive body 255 remains supported by first andsecond end sections 257-258 remaining on the first and second sides231-232, respectively, of the trench 230 (see FIG. 22). Thus, a cut canbe made through the second light-transmissive body 255 at a specificlocation 299 near the first side 231 of the trench 230 such that thecenter section 256 becomes unsupported and, as a result, the centersection 256 curves downward (i.e., bends) into the trench 230, therebyforming the second segment 222 of the optical waveguide 220, wherein thefirst portion 223 of the second segment 222 corresponds to the centersection 256 of the second light-transmissive body 255, which bends intothe trench 230, and the second portion 224 of the second segment 222corresponds to the second end section 258 of the secondlight-transmissive body 255, which remains on the top surface 282 of thesecond dielectric layer 212 on the second side 232 of the trench 230(1224, see also FIGS. 22-23 in combination).

It should be noted that, in this case before the secondlight-transmissive body 255 is cut, specific dimensions of the secondlight-transmissive body 255, the cut and the trench 230 as well as thespecific location 299 of the cut should be determined to ensure that,when the trench 230 is formed and when the second light-transmissivebody 255 is cut and the center section 256, which is now unsupported,bends downward, the center section 256 lands on the bottom 235 of thetrench 230 in end-to-end alignment with the first segment 221 eitherimmediately adjacent to or at least less than a predetermined distance295 from the end 227 of the first segment 221. The predetermineddistance 295 can be the maximum separation distance allowable for lightto propagate between the segments. Those skilled in the art willrecognize that this maximum separation distance will vary depending upona variety of factors including, but not limited to, the materials used,the cross-sectional area of the segments, the frequency of the lightsignals, etc. The dimensions can include, but are not limited to, thecross-sectional area of the second light-transmissive body 251, thewidth and height of the second light-transmissive body 255, the specificlength of the center section 256 of the second light-transmissive body255 that will be unsupported over the trench 230, the specific distance290 by which the center section 256 should overlay the first segment221, the length of the trench 230 and the depth of the trench 230 (i.e.,the thickness of the second dielectric layer 212). The expressions(1)-(3), discussed above, can similarly be used to estimate thedeflection of the unsupported center section.

It should also be noted that the remaining portion 225 of the first endsection 257 of the second light-transmissive body 255 (as shown in FIG.23), which is separated from the center section 256 as a result of thecut and which remains on the second dielectric layer 212 at the firstside 231 of the trench 230 above the first segment 221 of the opticalwaveguide 220, could be selectively removed. Alternatively, thisremaining portion 225 of the first end section 257 can be incorporatedinto another single or multi-level waveguide.

In any case, after the second segment 222 is formed, a third dielectriclayer 213 can formed (e.g., deposited) over the top surface 282 of thesecond dielectric layer 212 (1226, see also FIG. 2). Specifically, thethird dielectric layer 213 can be formed so that it covers the secondportion 224 of the second segment 222 of the optical waveguide 220 onthe top surface 282 of the second dielectric layer 212 adjacent to thesecond side 232 of the trench 230 (and, if applicable, any remainingportion 225 the first end section 257 on the top surface 282 of thesecond dielectric layer 212 adjacent to the first side 231 of the trench230) and also so that it fills the trench 230 and covers any exposedsurfaces of the first portion 223 of the second segment 222 of theoptical waveguide 220 contained within the trench 230. After the thirddielectric layer 213 is deposited, an optional chemical-mechanicalpolishing (CMP) step may be performed in order to ensure that the topsurface of the third dielectric layer 213 is essentially planar.

As mentioned above, the first and second segments 221-222 of the opticalwaveguide 220 can have specific refractive indices and, if thelight-transmissive material(s) used to form the two discrete segments,as discussed above, are the same, the refractive indices will be thesame. Furthermore, to ensure proper transmission of light signalsthrough the resulting optical waveguide 220, the refractive indices ofthe first and second segments 221-222, which function as the core of theoptical waveguide 220, must be higher than the refractive indices of thesurrounding dielectric material (i.e., which functions as the claddingof the optical waveguide 220). That is, the first and second segments221-222 should be formed so that they comprise light-transmissivematerial(s) (e.g., light-transmissive dielectric materials) with ahigher refractive index than the first dielectric layer 211, the seconddielectric layer 212 and the third dielectric layer 213.

Optionally, the first dielectric layer 211 formed at process 1204, thesecond dielectric layer 212 formed at process 1210, the third dielectriclayer 213 formed at process 1226 and/or any additional dielectric layers(e.g., formed on the substrate 201 before formation of the firstdielectric layer 211 or formed above the third dielectric layer 213) cancomprise different dielectric materials. For example, the firstdielectric layer 211 formed at process 1204 can comprise a firstdielectric material and the second dielectric layer 1212 formed atprocess 1210 can comprise a second dielectric material, which isdifferent from the first dielectric material and which, duringprocessing and, particularly during trench formation at process 1216 or1222 can be selectively etched over the first dielectric material.Furthermore, the second dielectric layer 212 formed at process 1210, thethird dielectric layer 213 formed at process 1226 and any additionaldielectric layer(s) 214 can comprise the same dielectric material ordifferent dielectric materials.

Therefore, in one exemplary method of forming the optoelectronicstructure 200, the first dielectric layer 211 can comprise siliconnitride, having a refractive index of approximately 2; the seconddielectric layer 212, third dielectric layer 213 and an additionaldielectric layer 214 between the substrate 101 and the first dielectriclayer 211 can comprise silicon dioxide, having a refractive index ofapproximately 1.5; and, the light-transmissive layers used to form thefirst segment 221 and second segment 222 can comprise silicon (Si)having a refractive index of approximately 3.5 or any of the followingmaterials having even higher refractive indices: phosphorous-dopedand/or boron-doped silicon oxide, germanium-doped silicon oxide, siliconoxynitride (SiON), silicon germanium (SiGe), or any of various differentlight-transmissive polymers. It should be understood that the list ofexemplary materials mentioned above is not intended to be limiting.Those skilled in the art will recognize that, alternatively, othermaterial combinations suitable for use in optoelectronic structures and,particularly, suitable for use as core and cladding materials in opticalwaveguides could be used.

Each method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should be understood that the terminology used herein is for thepurpose of describing the disclosed structures and methods and is notintended to be limiting. For example, as used herein, the singular forms“a”, “an” and “the” are intended to include the plural forms as well,unless the context clearly indicates otherwise. Additionally, as usedherein, the terms “comprises” “comprising”, “includes” and/or“including” specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. Furthermore, asused herein, terms such as “right”, “left”, “vertical”, “horizontal”,“top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”,“over”, “overlying”, “parallel”, “perpendicular”, etc., are intended todescribe relative locations as they are oriented and illustrated in thedrawings (unless otherwise indicated) and terms such as “touching”,“on”, “in direct contact”, “abutting”, “directly adjacent to”, etc., areintended to indicate that at least one element physically contactsanother element (without other elements separating the describedelements). The corresponding structures, materials, acts, andequivalents of all means or step plus function elements in the claimsbelow are intended to include any structure, material, or act forperforming the function in combination with other claimed elements asspecifically claimed.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

Therefore, disclosed above are optoelectronic structures, each having anoptical waveguide comprising two discrete segments that provide amulti-level optical signal pathway on a chip. The optical waveguide cancomprise a first segment at a first level and a second segment, whichextends between the first level and a higher second level and whichfurther extends along the second level. Specifically, the opticalwaveguide can comprise a first segment between a first dielectric layerand a second dielectric layer. A trench can extend through the seconddielectric layer such that it has a first side positioned laterallyadjacent to one end of the first segment and such that it has a secondside opposite the first side. The optical waveguide can further comprisea second segment with a first portion and a second portion. The firstportion can be within the trench and can extend from the first side onthe bottom adjacent to the first segment up to the top on the secondside. The second portion can be continuous with the first portion andcan extend laterally onto the top surface of the second dielectriclayer. A third dielectric layer can cover the second segment both in thetrench and on the top surface of the second dielectric layer. Alsodisclosed herein are methods of forming such optoelectronic structures.

What is claimed is:
 1. An optoelectronic structure comprising: a firstdielectric layer; a first segment of an optical waveguide on said firstdielectric layer; a second dielectric layer on said first dielectriclayer and covering said first segment, said second dielectric layerhaving a bottom surface, a top surface opposite said bottom surface, anda trench extending from said top surface to said first dielectric layerand having a first side and a second side opposite said first side, saidfirst side being adjacent to a first end of said first segment; a secondsegment of said optical waveguide comprising: a first portion having asecond end in end-to-end alignment with said first end of said firstsegment at said first side, said first portion further directlycontacting said first dielectric layer at a bottom of said trench andextending through said trench from adjacent to said first segment atsaid first side to said top surface at said second side; and, a secondportion continuous with said first portion, said second portion being onsaid top surface adjacent to said second side; and a third dielectriclayer on said top surface of said second dielectric layer, on saidsecond portion, and within said trench covering said first portion, saidfirst segment and said second segment each having a higher refractiveindex than said first dielectric layer, said second dielectric layer andsaid third dielectric layer; said second end of said first portion ofsaid second segment being physically separated from said first end ofsaid first segment and being positioned less than a predetermineddistance from said first end of said first segment.
 2. Theoptoelectronic structure of claim 1, said trench having a first sidewallon said first side and a second sidewall on said second side, said firstsidewall and said second sidewall being angled relative to said bottomof said trench such that said first sidewall and said second sidewallare not perpendicular relative to said bottom, said first portion ofsaid second segment lining said bottom of said trench and said secondsidewall such that said first portion of said second segment isimmediately adjacent to a portion of said first dielectric layer at saidbottom of said trench and extends laterally from said first segment tosaid second sidewall and such that said first portion of said secondsegment is also immediately adjacent to said second sidewall from saidbottom of said trench to said top surface of said second dielectriclayer.
 3. The optoelectronic structure of claim 1, said trench having afirst sidewall on said first side and a second sidewall on said secondside, said first portion of said second segment being immediatelyadjacent to a portion of said first dielectric layer at a bottom of saidtrench, and said first portion further extending laterally from saidfirst segment at said first side toward said second sidewall and curvingupward away from said bottom of said trench to said top surface of saidsecond dielectric layer such that a distance between said first portionand said second sidewall tapers from said bottom of said trench to saidtop surface of said second dielectric layer.
 4. The optoelectronicstructure of claim 1, said first dielectric layer and said seconddielectric layer comprising different dielectric materials.
 5. Theoptoelectronic structure of claim 1, said second dielectric layer andsaid third dielectric layer comprising any one of a same dielectricmaterial and different dielectric materials.
 6. The optoelectronicstructure of claim 1, said first segment having a first thickness, saidsecond segment having a second thickness that is essentially equal tosaid first thickness, and said second dielectric layer having a thirdthickness that is greater than said first thickness and said secondthickness.
 7. An optoelectronic structure comprising: a first dielectriclayer; a first segment of an optical waveguide on said first dielectriclayer; a second dielectric layer on said first dielectric layer andcovering said first segment, said second dielectric layer having abottom surface, a top surface opposite said bottom surface, and a trenchextending from said top surface to said first dielectric layer andhaving a first side and a second side opposite said first side, saidfirst side being adjacent to a first end of said first segment, saidtrench having a bottom, a first sidewall on said first side and a secondsidewall on said second side; a second segment of said optical waveguidecomprising: a first portion lining said bottom of said trench and saidsecond sidewall such that said first portion has a second end inend-to-end alignment with said first end of said first segment at saidfirst side, directly contacts said first dielectric layer at said bottomof said trench and extends through said trench from adjacent to saidfirst segment at said first side, along said bottom of said trench, andfurther along said second sidewall of said trench to said top surface atsaid second side; and, a second portion continuous with said firstportion, said second portion being on said top surface adjacent to saidsecond side; and a third dielectric layer on said top surface of saidsecond dielectric layer, on said second portion and within said trenchcovering said first portion, said first segment and said second segmenteach having a higher refractive index than said first dielectric layer,said second dielectric layer and said third dielectric layer; saidsecond end of said first portion of said second segment being physicallyseparated from said first end of said first segment and being positionedless than a predetermined distance from said first end of said firstsegment.
 8. The optoelectronic structure of claim 7, said second segmentbeing physically separated from at least an upper portion of said firstsidewall.
 9. The optoelectronic structure of claim 7, said firstsidewall and said second sidewall being angled relative to said bottomof said trench such that said first sidewall and said second sidewallare not perpendicular relative to said bottom.
 10. The optoelectronicstructure of claim 7, said first dielectric layer and said seconddielectric layer comprising different dielectric materials.
 11. Theoptoelectronic structure of claim 7, said second dielectric layer andsaid third dielectric layer comprising any one of a same dielectricmaterial and different dielectric materials.
 12. The optoelectronicstructure of claim 7, said first segment having a first thickness, saidsecond segment having a second thickness that is essentially equal tosaid first thickness, and said second dielectric layer having a thirdthickness that is greater than said first thickness and said secondthickness.
 13. An optoelectronic structure comprising: a firstdielectric layer; a first segment of an optical waveguide on said firstdielectric layer; a second dielectric layer on said first dielectriclayer and covering said first segment, said second dielectric layerhaving a bottom surface, a top surface opposite said bottom surface, anda trench extending from said top surface to said first dielectric layerand having a first side and a second side opposite said first side, saidfirst side being adjacent to a first end of said first segment, saidtrench having a bottom, a first sidewall on said first side and a secondsidewall on said second side; a second segment of said optical waveguidecomprising: a first portion having a second end in end-to-end alignmentwith said first end of said first segment at said first side, said firstportion further directly contacting said first dielectric layer at abottom of said trench, extending laterally from adjacent said firstsegment at said first side toward said second side and further curvingupward away from said bottom of said trench to said top surface of saidsecond dielectric layer at said second side, said first portion beingphysically separated from said second sidewall with a distance betweensaid first portion and said second sidewall tapering from said bottom ofsaid trench to said top surface of said second dielectric layer; and, asecond portion continuous with said first portion, said second portionbeing on said top surface adjacent to said second side, said firstsegment having a first thickness, said second segment having a secondthickness that is essentially equal to said first thickness, and saidsecond dielectric layer having a third thickness that is greater thansaid first thickness and said second thickness; and, a third dielectriclayer on said top surface of said second dielectric layer, on saidsecond portion and within said trench covering said first portion andfilling a space between said first portion and said second sidewall,said first segment and said second segment each having a higherrefractive index than said first dielectric layer, said seconddielectric layer and said third dielectric layer; said second end ofsaid first portion of said second segment being physically separatedfrom said first end of said first segment and being positioned less thana predetermined distance from said first end of said first segment. 14.The optoelectronic structure of claim 13, said second segment beingphysically separated from at least an upper portion of said firstsidewall.
 15. The optoelectronic structure of claim 13, said firstsidewall and said second sidewall being one of angled and curvedrelative to said bottom of said trench such that said first sidewall andsaid second sidewall are not perpendicular relative to said bottom. 16.The optoelectronic structure of claim 13, said first dielectric layerand said second dielectric layer comprising different dielectricmaterials.
 17. The optoelectronic structure of claim 13, said seconddielectric layer and said third dielectric layer comprising any one of asame dielectric material and different dielectric materials.